1. Field of the Invention
The present invention relates to a coating method and apparatus and, particularly relates to a coating method and apparatus for applying a coating fluid onto a continuously running flexible support.
2. Description of the Prior Art
Heretofore, the application of a coating fluid having suitable fluidity onto a running flexible support for manufacturing industrial goods, for example, produced by use of magnetic coating fluid, photographic light-sensitive coating fluid, pressure-sensitive coating fluid, thermo-sensitive coating fluid or the like, has been employed due to superior productivity of conventional methods and apparatus.
For example, in the case of manufacture of magnetic recording media such as magnetic tape, there are various kinds of methods, such as those described in Japanese Patent Unexamined Publication Nos. 57-84771 and 58-104666, which uses a coating apparatus with a doctor edge surface 5a composed of two planes as shown in FIG. 6, and those described in Japanese Patent Unexamined Publication No. 59-94657, which uses a coating apparatus with a doctor edge surface 5a having a curved surface so that a tangent can be drawn from the downstream end of a back edge 6 to the doctor edge surface 5a as shown in FIG. 7.
However, in the case where the coating apparatuses having the aforementioned edge forms are employed, the allowable range of thickness of coating film which can be obtained changes in accordance with changes in factors such as the application speed, the physical properties of coating fluid (in particular, viscosity), the thickness of the support, and the like. A problem exists in that the coating apparatuses having such edge forms cannot be used for producing multiple various kinds of articles, since the required film thickness for such articles often is not within allowable thickness range achievable using these edge forms. Alternatively, the productivity of such coating apparatuses is very low even though the required film thickness may be obtained for a small percentage of the samples. Although coating apparatuses capable of producing a necessary film thickness can be provided by changing the edge form, such a procedure is disadvantageous in that the cost increases due to the time needed for frequent preparation of the extruders corresponding to the necessary film thickness, and a great deal of labor is required for searching the allowable film thickness range peculiar to each coating apparatus. The problem is not limited, to the case where different kinds of articles are manufactured. The same problem exists in the case where the coating thickness is changed in the same article and in the same allowable film thickness range.